The present invention relates to a print head driving apparatus driving a print head based on inputted print data and a printer using the same.
Conventionally, previous apparatus is one driving an LED chip in which many LEDs (light emitting devices) though not shown. The print head driving apparatus having a plurality of AND circuits and switches, a processing unit including a D/A converter and the like, a shift register connecting to this processing unit and internally divided into an m-bit shift register and an n-bit shift register which receive data, a latch circuit latching printing data received by the m-bit shift register, a latch circuit latching printing data received by the n-bit shift register and a switch circuit which can switch a single use mode in which only the m-bit shift register is used to/from a combination use mode in which the m-bit shift register and the n-bit shift register are used in combination with each other.
In the above apparatus, in the combination use mode switched by the switch circuit, m-bit printing data adjusting data and n-bit printing data adjusting data are latched by different timing and the LED chip is driven by drive signals at different timing.
However, if a plurality of print head driving apparatuses are used to drive a long line head as in the case of a conventional apparatus in which a shift register is divided into a plurality of registers, it is necessary to change drive timing for the respective driving apparatuses due to mechanical limitations and so on. In addition, if a so-called tandem type color printer provided with a printing unit for printing data with Yellow, Magenta, Cyan and Black is to be realized by using the conventional head driving apparatus, different head driving apparatuses for the printing units for the respective colors are required. This applies to not only a case where line heads of the respective colors are driven by a plurality of head driving apparatuses but also a case where they are driven by a single head driving apparatus. Further, the head driving apparatuses corresponding to the printing units of respective colors should be driven differently since it is necessary to latch print data at different timing and to carry current to thereby print the data.
For these reasons, the conventional apparatus has disadvantages in that latch signals (LACH) and driving signals in addition to printing data should be transmitted to the head driving apparatuses, respectively, a head control section controlling the head driving apparatuses requires many control lines and connectors for connection should be of multi-pin type.
Moreover, even if a single head driving apparatus drives a single line head, too many control lines and connectors are used. Thus, the conventional apparatus has disadvantage in that cost reduction cannot be sufficiently realized.
It is an object of the present invention to provide an inexpensive print head control apparatus capable of reducing the number of signal lines necessary to control a head driving apparatus, capable of driving print heads without increasing signal lines even if the print heads differ in printing timing and capable of reducing the number of IC pins in a head control section controlling the head driving apparatus, the number of communication cables and connector pins for connecting the head driving apparatus to the head control section, and to provide a printer using this apparatus.
The present invention is a print head driving apparatus including input means for inputting serial data including printing data and timing data put in the printing data; extracting means for detecting the timing data included in the serial data inputted by the input means and for extracting the printing data from the serial data with the detected timing data as a starting point; and output means for outputting a driving signal for driving a print head for printing based on the printing data extracted by the extracting means.
According to the present invention constituted as stated above, there is no need to independently provide timing of the register and latching timing of the latch circuit, a timing signal of one bit or more put in the printing data is detected and the printing data, which is the serial data, is latched based on this timing signal. Thus, it is possible to realize cost reduction and to make an apparatus smaller in size by reducing signals necessary for the print head driving apparatus.
Further, the present invention is worked by many other embodiments showing modifications including, for example, a case where no latch signal is needed by providing an enable signal, a case where a plurality of print head driving apparatuses are cascade-connected, a case where a counter is replaced by an inverter and a case where a plurality of print head driving apparatuses are specified for a plurality of color print heads.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.